1. Field of the Invention
The present invention relates to hot-melt adhesive compositions for the coating of sheet structures, for example textiles, leather, foam materials or polymer films. The present invention relates in particular to hot-melt adhesive compositions for the patternwise coating of bondable interlining materials for the clothing industry, especially for outer clothing.
2. Discussion of the Background
Hot-melt adhesive compositions are known which are preferably applied in a pattern, in the form of an aqueous paste, to a sheet structure to be coated. Drying and sintering are then carried out. The sintered product constitutes the hot-melt adhesive composition. The coated sheet structures are laminated, in sheet form or cut to shape, with other sheet structures in sheet form or cut to shape, under the action of pressure and a comparatively mild temperature to give cleaning-resistant laminates having a particularly high degree of wash resistance and adhesion.
Numerous hot-melt adhesive compositions having cleaning-resistant properties are known for use in screen-printing. These are principally formed from aqueous-pasty mixtures comprising fine hot-melt adhesive powders, which can also be employed per se, in coarser granular form, directly for coating by the scatter or powder dot method. The cleaning-resistant hot-melt adhesive compositions most in use today are based on copolyamides, copolyesters or low-pressure polyethylene. Other hot-melt adhesive compositions which are likewise used are not resistant to cleaning.
To form a paste from the fine hot-melt adhesive powders, in order to produce the adhesive layer, special suspension agents or dispersants are used which allow the pastes to be printed cleanly without reducing the resistance to cleaning. In addition, dispersants are intended to give rise to particular features in terms of properties, for example the prevention of sedimentation of the powders incorporated by mixing, a print with well-defined contours, controlled penetration of the hot-melt adhesive paste, prevention of penetration by the outer material, the avoidance of recoiling in the course of bonding, or the prevention of the edges becoming welded together while the sheet structures are being cut to shape. Examples of such dispersants have been described, for example, in U.S. Pat. Nos. 3,956,213, 4,237,040 and 4,272,566. Plasticizers can be added to the dispersants. In many cases, further additives comprising high molecular weight polyethylene oxide are added, which increase the spreadability of the paste.
For coating in a pattern by the screen-printing technique, screen-printing stencils are used which have a regular or irregular arrangement of perforations through which hot-melt adhesive compositions are pressed onto the interlining material using an internal doctor blade. Whereas, formerly, screen stencils were used which had a comparatively wide spacing and large apertures, for example 17 mesh, in recent times coatings of increasing fineness have been carried out with a close sequence of smaller apertures, for example 30 mesh, with the formation of small, closely adjacent dots of hot-melt adhesive. Moreover, the interlining materials have become more lightweight, finer and more open. The problems associated with coating have grown as the patterns have become finer, and the cleaning and washing problems have increased at the same time, since the larger pattern arrangement with larger individual dots produced a greater adhesive strength than the finer pattern arrangement with relatively small individual dots.
However, the use of interlining materials has also experienced a gradual change. For reasons of fashion and, probably, of environmental protection as well, there is increasing use in articles of clothing of interlining materials which have been or are to be washed rather than cleaned, for example interlinings for leisure wear.
This change in trends has led to the gradual replacement of copolyamide hot-melt adhesives which were originally used exclusively for articles of outer clothing by copolyesters, since copolyesters--although not having the particularly good dry-cleaning resistance of the copolyamides--nevertheless possess a better resistance to washing. Low-pressure polyethylenes are excluded because of the excessive bonding temperatures.
Costs and quality issues have dictated a marked reduction in the quantity of coating which is applied per m.sup.2 of interlining material. Whereas, formerly, add-ons of from 18 to 25 g/m.sup.2 were common, they are nowadays from 7 to 15 g/m.sup.2, to meet the need for a soft, flowing drape of the bonded articles of clothing.
In order to solve the problems relating to the reduced washing and cleaning resistance and to the weaker adhesion, improved hot-melt adhesive compositions and also improved coating technologies were developed. Dual-dot or double-dot coatings are described, for example, in patents DE-B 22 14 236, DE-B 22 31 723, DE-B 25 36 911, and DE-B 32 30 579. Moreover, patents EP-A 0 219 376 and EP-A 0 365 711, describe an indirect coating method.
The coating substrates were improved by using finer yarns having individual fibers of finer denier, ranging down to the microfiber region, and synthetic yarns, for example high-bulk acrylic yarns and crimped polyester yarns. Moreover, the fabrics originally used have been replaced by other sheet structures, for example by weave-knit products or by weave-knit bonded fibre webs and stitch-bonded webs, the latter materials representing a combination of bonded fibre webs with knitted fabrics.
Deficiencies which continue to exist are seen, in particular, in a stiffening and in a reduced crease-resistance of a bonded laminate of interlining and outer material, especially in the case of finely patterned coatings. A factor regarded as being particularly negative, however, is that, in fine-coated interlining materials on fine outer materials, for example blouse outer materials, and despite the use of polyesters, the wash resistance of the bonded laminate is no more than moderate and in many cases is even deficient. There therefore continues to be a considerable need for an interlining of low coating weight which can be applied by hot pressing at the mild fixing temperatures which are nowadays conventional and which imparts a soft bonded handle, can be washed without any problems and retains a high adhesive strength after the washing procedure.
In particular, there is a great need for such interlinings in women's outer wear. Here in particular, depending on fashions, outer materials which lend themselves very unreadily to bonding, such as silk, polyester viscose georgette and siliconized or fluorocarbonized outer materials, are processed. The current interlinings achieve very good primary adhesion, but after washing or cleaning complete detachment occurs. Even complex coating methods such as the traditional double dot and indirect coating techniques bring hardly any success in this context.